Waste treatment process

ABSTRACT

In a process for the treatment of at least one mixture of solid and liquid waste substances which contains at least one metal such as Fe and/or compounds thereof, for example oxides, the mixture occurring in a condition in which it can be used at least only with difficulty, the mixture is at least extensively homogenized and mixed with at least one very fine-grain dry substance containing fly ash and/or coke. The resulting mixture is of such a nature, for example being at least predominantly in the form of agglomerates, that it can be fed to a thermal procedure, possibly after a grading operation.

This is a continuation of a copending application Ser. No. 07/825,392filed on Jan. 24, 1992.

BACKGROUND OF THE INVENTION

The invention concerns a process for the treatment of wastes, involvinga first mixture of solid and liquid waste materials, which contains atleast one metal such as Fe and/or compounds thereof, for example oxides,in such a condition that it cannot be used or can be used only withdifficulty.

It is known for waste materials to be subjected to treatment, the aim ofwhich is to put them into a condition in which they can be handled. Thusfor example DE 32 08 699 C2 discloses a process for the production ofgranulated copperas--FeSO₄.7H₂ O. The latter is a waste product which isproduced primarily in the manufacture of titanium dioxide. WithpH-values of between 1 and 2, it is highly acid. It has a tendency tocake together so that it can only be removed from storage containerswith considerable difficulty. The procedure involves mixing copperaswith dried brown coal or lignite in dust form, in such an amount thatthe resulting mixture is capable of a trickle flow. Copperas is arelatively homogeneous waste material. That procedure is expensive asbrown coal or lignite dust which may have only a low water contentrepresents an expensive material. DE 32 15 727 Al discloses a processfor the treatment of red mud which is a waste product that is producedin the production of aluminium in the form of iron oxide (Fe₂ O₃, Fe ₃O₄), being present in the form of an alkaline aqueous suspension. Thatsuspension is filtered, with the red mud being deposited on the filtercloth. That procedure provides that the red mud is mixed with coal dust,more especially brown coal or lignite dust, in order to produce amixture which is capable of trickle flow. That procedure is alsoexpensive, especially as comparatively large amounts of coal dust mustbe used in order to produce the desired effect of a mixture which iscapable of trickle flow. Red mud however is also a comparativelyhomogeneous waste product.

Many areas of industry involve the production of waste products whichare substantially less homogeneous, as they frequently represent amixture consisting of a plurality of solid and liquid components. Atypical product of that kind is rolling scale slurry or sludge. Rollingscale is for example the oxidation layers which are produced whenrolling and forging steel and when drawing wire. In the rolling mill,the rolling scale is swept off the rolled surface of the metal duringthe rolling operation, for example by means of a jet of water. The wastewater which is charged with fine-grain rolling scale collects beneaththe roll stand in the scale pit in which the roll scale slurry isdeposited; the roll scale slurry, besides the metal oxide and water,also contains impurities due to carbon-bearing lubricants and allpossible objects and articles which are thrown away in operation of therolling mill. At any event, as regards the finer-grain constituents ofthe rolling scale slurry or sludge, the latter is extremely difficult tohandle so that in general it is not re-used, although its high contentof iron oxide means that it would represent a valuable startingmaterial. However, recycling for example to a metallurgical procedurewould also involve taking account of the content of lubricant materials.Thus rolling scale slurry may contain for example more than 5%lubricating oil or the like so that it is not normally possible to treatthe rolling scale slurry for example by sintering, as the combustionproducts which result from the oil components in the sintering operationgive rise to problems.

Other waste materials which give rise to difficulties in regard tore-use thereof are sludges which originate from the production of ironoxide for the manufacture of ink or dye pigments, and black sludge whichis produced in the manufacture of aluminum and which essentiallycomprises Al₂ O₃, carbon predominantly in the form of graphite andbetween 35 and 40% water. The re-use of blast furnace flue gas dusts,blast furnace flue gas slurries or sludges, sinter dusts, converterdusts, converter sludges and foundry dusts which are produced inmetallurgical works, as well as grinding dusts, grinding slurries andsludges, and dusts and sludges originating from cutting machiningoperations, also give rise to difficulties as they frequently occur inthe form of a mixture which is difficult to handle or which also cannotbe directly re-used.

Difficulties in terms of handling further arise by virtue of the factthat the above-indicated waste materials and waste mixtures occur invery different compositions and thus involve different consistencies.The mixtures are frequently also highly heterogeneous, for example dueto the foreign objects which are contained in rolling scale sludge andwhich may also involve small pieces of waste from the rolled material;the fact that the mixtures are highly heterogeneous also makes itdifficult to subject them to suitable treatment steps to produce ahandleable product which can be re-used.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a process for thetreatment of waste, such that waste products which differ in terms oftheir composition and/or consistency and/or moisture content and/orimpurities contained therein and which fluctuate in respect ofcomposition and consistency can be put into a re-usable form by suitabletreatment.

Another object of the present invention is to provide a waste treatmentprocess such that the resulting product is put into a condition such asto permit it to be handled without difficulty.

Still another object of the present invention is to provide a wastetreatment process which puts the waste material into a condition suchthat it can be re-utilised, with at least only a small amount of residueremaining after the process.

A still further object of the present invention is to provide a wastematerial treatment process which can be operated in an inexpensivefashion, not least also in regard to the substances or mixtures whichare to be added to the waste material to be treated and which serve tovary the consistency thereof.

Yet a further object of the present invention is to provide a processfor the treatment of a mixture of solid and liquid waste materials,involving the addition of substances thereto, which additionalsubstances in turn also represent waste materials which in that way arerecycled.

Still a further object of the present invention is to provide a processfor the treatment of a mixture of solid and liquid waste materials,involving the addition thereto of treatment substances which as far aspossible exhibit neutral characteristics in the context of the processor even have an advantageous effect on the procedures which take placein the treatment process.

In accordance with the present invention the foregoing and other objectsare achieved by a process for the treatment of a first mixture of solidand liquid waste materials, which contains at least one metal, forexample Fe, and/or at least one compound thereof, for example an oxide,the mixture occurring in a Condition in which it cannot be used or canbe used only with difficulty, wherein the mixture is at leastextensively homogenised and wherein at least one very fine-grain drysubstance which has fly ash and/or coke is added thereto and mixedtherewith in such an amount that the resulting mixture occurs at leastpredominantly in the form of aggregates of which at least a part can befed to a thermal procedure for re-utilisation thereof. The procedure canbe such that the dry substance which has fly ash and/or coke is added toand mixed with the first mixture in such an amount that the resultingmixture is of a nature which permits grading or classification thereof,the grading or classification operation producing at least one fractionwhich can be fed to a thermal procedure for re-utilisation thereof.

The use of fly ash has a number of advantages. On the one hand, fly ashfor a large part itself represents a waste product which can bere-utilised when carrying into effect the teaching in accordance withthe invention. Fly ash which is generally deposited in electricalfilters from gases such as more specifically flue gases is in dust formand is thus of extremely fine-grain nature so that, by virtue of itshigh specific surface area, it is capable of binding a very large amountof moisture. Furthermore in many cases fly ash includes constituents,for example and more especially CaO and MgO which advantageouslyinfluence the progress of the above-mentioned subsequent thermalprocedure.

The use of coke can be considered more especially when it is also indust form as coke dust is an inexpensive product which cannot be readilyused for other purposes. However the use of fly ash will be preferred inmany situations, especially as it occurs at a very large number oflocations when cleaning for example flue gases and other gases, so thatthe expenditure involved in transporting it to the location at which thetreatment is to be effected is in many cases less than when using coke.

The amount of flue ash and/or coke which is to be added to therespective first mixture and the duration of the mixing time essentiallydepend on the composition and the consistency of the first mixture. Thatmixing operation will additionally in general terms simultaneouslyinvolve homogenisation of the first mixture. It may however also bedesirable or even necessary to effect homogenisation of the firstmixture of waste materials prior to mixing with the substance orsubstances containing fly ash and/or coke. That may be the case forexample when the first mixture of waste material has been stored for aprolonged period of time so that the individual components of themixture have separated from each other or individual components havesettled out.

In accordance with a preferred feature of the invention, the operatingprocedure may be such that added to the first mixture of waste materialis a second mixture of liquid and/or solid waste material, the secondmixture occurring in a different condition from the first mixture, atleast in regard to moisture content and/or grain size. Handling in thatway may be desirable for example when dealing with residues from thepigment industry for ink or dye production. Thus, iron oxide is used asa pigment, that is to say as a base material for the production of redor black inks or dyes. In that respect, similar residues occur in termsof composition, namely Fe-bearing oxidic residues from the settlementbasin or vessel and Fe-bearing oxidic residues in the form of filterpastes and filter cakes. The residues from the settlement basin form agrainy, moist, black sludge or slurry, the grains of which predominantlycomprise iron oxide. The filter residues form a moist sludge or slurrywhich however is smudgy and compact. Both residues can be mixed togetherin order in that way to give a resulting mixture which is then mixedwith fly ash and/or coke.

It is also possible to operate in a corresponding fashion when treatingrolling scale sludges which may occur in different consistencies forexample in dependence on the works from which they originate. Here tooit is possible to mix a first mixture of a rolling scale sludge with asecond mixture of such a sludge, while fly ash and/or coke may be addedto the first mixture and/or the second mixture and/or the mixture of thefirst and second mixtures.

The two examples referred to above make use of mixtures which are atleast substantially the same as each other in regard to theircomposition of material. It should be appreciated however that theinvention can also be brought into effect if the first mixture and thesecond mixture are also clearly different from each other in terms ofcomposition. Thus it is possible to use a rolling scale sludge as thefirst mixture and for example residues from the pigment industry as thesecond mixture, or vice-versa. It is also possible for the first mixtureand/or the second mixture to represent mixtures made up of at least twostarting mixtures.

The amount of fly ash and/or coke which is added to the first and/or thesecond mixture and/or the mixture resulting from the first and secondmixtures depends on the respective parameters involved, for example andmore especially the moisture content of the mixture and the compositionand grain size of the additive substances. The amount involved can beascertained by means of simple tests. It is to be so selected that, inthe course of the mixing operation, agglomerates are formed which makeit possible for the resulting mixture to be classified or graded forexample by sieving in order in that way to remove foreign bodies whichare present in the initial mixtures, for example paper, cleaning rags,bottles, pieces of wood, pieces of iron, metal cans, plastic foils andthe like. The waste mixtures are not sievable in the original condition.Thus in the case of rolling scale sludge of a given consistency therequired proportion of fly ash may be between 30 and 35% by weight ofthe moist rolling scale sludge. When dealing with the same rolling scalesludge, different amounts may be required in order to achieve thedesired effect, when using coke or a fly ash of a different origin. Inall situations the moisture content of the waste material mixture is sostrongly bound by the fly ash and/or the coke that the above-mentionedagglomerates are formed; the agglomerates do not cling together or theycling together only to such a slight extent that classification orgrading thereof for example by sieving is possible. The addition of flyash and or coke avoids in particular the application of energy fordrying the waste material mixture.

One or more further components in the waste material mixture include forexample blast furnace gas dust, blast furnace gas sludge, sinter dust,converter dust, converter sludge, grinding dust, grinding sludge,foundry dust as well as dusts and sludges from cutting machining forexample of metals. In that respect it is possible for theabove-mentioned component or components also to contribute to bindingthe moisture in the initial mixture involved.

When using coke in a fine and/or very fine grain size for treatment ofthe first and/or second mixture, the C-content of the resulting mixtureis thereby increased at the same time. That may have the advantage thatin that way the carbon requirement of a subsequent process forre-utilisation of the material is entirely or partially met.Furthermore, irrespective of the treatment applied to the first and/orsecond mixture by the addition of fly ash and/or coke for the purposesof forming agglomerates and/or to make the material capable of beinggraded or classified, it is readily possible additionally to add cokeand/or coal in a fine or very fine grain size, in order to adjust theC-content. It can be considered that also results in certain amounts ofmoisture in the first and/or second mixture being bound, although thatdoes not normally occur to the extent as when using fly ash or cokedust, which may have a surface area of around 300 m² /g for example whenit is made from brown coal or lignite.

If the fly ash does not contain an adequate amount of CaO and/or MgO orat least one substance which acts chemically in the same fashion, it maybe desirable to add to the first mixture and/or the second mixtureand/or the resulting mixture, burnt lime or a substance or substanceswhich at elevated temperature gives burnt lime or at least one substancewhich chemically reacts in the same fashion. That will be desirable andpossibly even necessary in particular if the acidity of the mixturewhich is fed for re-utilisation in a thermal process may not exceed acertain value or if that mixture must in any case be basic. The use offly ash with such components is particularly appropriate at any event asit achieves the desired effect without additional expenditure due to theaddition of burnt lime or the like. In particular brown coal or ligniteashes are frequently basic.

The use of such fly ashes may also be advantageous in particular for thereason that the resulting agglomerates, after a certain period of time,set and consolidate due to a binding procedure so that, in contrast tothe starting material, they can be stored in the open air without anyfear of the risk of environmental pollution for example under the effectof rainwater. It is also possible for the small agglomerates which areproduced when carrying out the process according to the invention andwhich may be for example of a diameter of the order of magnitude of 4 mmto be pelletised to form larger agglomerates.

EXAMPLE

Further objects, features and advantages of the process in accordancewith the present invention will be more clearly apparent from thefollowing description of a preferred embodiment which involves thetreatment of residues from the pigment industry. When such wastematerials are stored in the open air, oxidation processes take place,with a corresponding amount of heat being produced, with the possibilityof temperatures of more than 100° C. occurring. Therefore, with thenormal requirements which are applied nowadays in regard to protectionof the environment, it is no longer possible for materials of that kindto be dumped without special precautions being taken.

When using the process in accordance with the invention, to deal withsuch waste materials as referred to above, it is desirable for themfirstly to be at least extensively homogenised. For that purpose the twowaste materials which may differ from each other in particular in regardto moisture content and grain size, more specifically residues from asettlement basin and residues in the form of filter pastes and filtercakes, are mixed together in such a way as to produce a substantiallyunitary, black, moist, pulpy to compact material. Dry fly ash is thenintroduced into that material and mixed therewith. The amount of fly ashadded depends on the desired nature of the resulting mixture made fromthe two initial mixtures of waste materials. That consideration alsoapplies in regard to the duration of the mixing operation. Bothparameters can be ascertained by simple testing, giving empirical valuesas to which quantities of fly ash and/or coke are required in relationto a given consistency of the mixture. It can generally be assumed thatthe moisture content of fly ash and/or coke is negligibly small in thiscontext.

In the course of the operation of admixing fly ash, the resultingmixture becomes friable or capable of trickle flow, with the formationof small agglomerates, so that it can be graded or classified forexample by sieving for the purposes of removal of coarser impurities.When using basic brown coal or lignite fly ash, the acidity of theresulting predominantly agglomerated material is greatly reduced. If flyash from pit coal firing operations is used, which is generally notbasic, lime may be added to the mixture for neutralisation purposes. Inthat way the lime requirement which may possibly be involved in asubsequent thermal procedure can also be entirely or partially met bythat addition.

The mixing ratio as between the first mixture which in this casecomprises residues from a settlement basin and the second mixture whichin this case comprises filter residues was about 3:1 in a specific case.With a delivery amount of 1000 kg, a mixing time of between 1 and 5minutes and preferably between 1 and 2 minutes was generally sufficientto homogenise a first mixture and a second mixture in a forced-actionmixer.

Thereupon additive substances were added to the mixture resulting fromthe first and second mixtures. Firstly, in relation to the amount ofsaid resulting mixture, between 10 and 20% of brown coal or lignite flyash was added, and mixed with the homogenised mixture in theabove-mentioned mixer. That already resulted in a mixture which was in afriable condition or a condition of being capable of trickle flow andwhich is of a neutral to slightly basic character. At any event themixture behaves neutrally in a subsequent metallurgical procedure. Itsslight basicity is insignificant. For the preparation of C for thesubsequent metallurgical process, it is possible to add brown coaland/or pit coal dusts or very fine-grain coke from such coals, forexample in a ratio of between 7 and 8%, once again in relation to thecharge amount of the first and second mixtures of waste materials.Whether and to what extent C-bearing dusts are added will depend on therespective circumstances involved, more especially the composition ofthe other substances which are fed to the thermal procedure.

Due to the addition of the very fine-grain fly ash with a hydraulicaction, a large part of the moisture contained in the mixture isinitially bound. Added to that there is the further effect that mixingwith the fine ash particles which are predominantly for example of agrain size of between 70 and 90 μm means that access on the part ofoxygen in the air to the Fe-oxide particles is made more difficult sothat further exothermic reaction thereof is at least greatly restricted.That is not least a consequence of the above-mentioned formation ofaggregates as that phenomenon reduces the effective surface area of theFe-oxide particles. Furthermore the particles of ash form a kind ofcasing or sheathing around the agglomerates, and that also greatlyreduces or prevents access of oxygen to the agglomerates. The sameconsideration also applies in regard to the addition of coke dust ofcorrespondingly fine grain size. Thus, it is possible to produce aresulting mixture consisting of coke dust and the first and secondmixture, which has similar properties to the resulting mixture which isobtained by the addition of fly ash. It will be noted than the additionof fly ash with pozzuolanic properties has the advantage that theagglomerates formed are bound and are thus made firmer.

In that case the resulting mixture can be pelletised. That is preferablyeffected after a grading or classification operation for the removal ofimpurities, foreign bodies and the like. Whether water must additionallybe added for the pelletisation operation depends inter alia on themoisture content of the agglomerates formed in the preceding mixingphase. Generally there will be a certain need for an additional amountof water. The pellets obtained in that way can be hardened by theapplication of heat and/or by storage so that if necessary they have thelevel of strength required for the subsequent metallurgical procedure.In this connection also it may be advantageous for the fly ash to havepozzuolanic properties as the reactions which take place are exothermicand the heat produced reduces the moisture content of the pellets. Thus,in a specific case, the initial temperature of the pellets was between100° and 120° C. After a storage time of 20 hours, the temperatures wereonly between 50° and 70° C. while after a storage time of 48 hours thetemperatures found were only between 18° and 35° C. The pellets formedin that way are then subjected to a pressure testing operation in orderto ascertain their strength. The results of that testing operation areset forth in Table I attached hereto. Those results show that, with thesize of the pellets, the compression strength thereof also increases, asis demonstrated in particular by the results of tests A through Mcontained in Table I.

As the pellets were all non-round, in order to ascertain their size, twomeasurements were taken in first and second directions identified as`d`, and `h`, which were perpendicular to each other. The temperature atwhich the compression strength testing operations were carried out was18° C.

Investigations were also carried out into the way in which the pelletsproduced behave in storage. A plurality of small beds or fills eachcontaining 40 kg of those pellets were sprayed in a roofed-over spacewith different amounts of water in order to check whether and to whatextent consolidation or crusting occurred. A small amount of crustingwas found at the surface of the respective bed or fill but the thicknessand hardness of the crusting was very slight. The crust could be easilyrubbed off between the fingers. In particular the pellets remained overa period of several weeks. The same results were obtained when using abed or fill of those pellets which were stored in the open air andexposed to rain. Those pellets were also still found to be capable offlow and suitable for pneumatic conveyance after having been stored inthe open air for some weeks.

Treatment of the waste materials by mixing with basic brown coal orlignite ash also affords considerable advantages in regard to thestorability of the resulting mixture or certain fractions thereof. Thatalso applies in particular in regard to residues from the production ofpigments, as they are frequently heavily charged with heavy metals andother undesirable components. If such residues are exposed to the actionof rain, they result in the formation of seepage waters which are highlyacid when it is untreated residues from pigment manufacture that areinvolved. They have a high level of demand for chemical oxygen.

After mixing with basic brown coal or lignite fly ash, the occurrance ofacid seepage waters was no longer observed when the resultingagglomerates were stored. On the contrary the seepage waters producedwere neutral to basic. When slightly alkaline seepage waters occurred,that can be attributed to the stored agglomerates. As a result of theelevated temperature of the agglomerates, which is to be attributed tothe above-mentioned exothermic reactions which take place, a part of therecycled water is evaporated so that it can be disposed of, withoutinvolving additional energy expenditure.

Set out in accompanying Table II are the results of analysis of twoelution tests which were carried out with two samples of residues frompigment manufacture. Those samples were not subjected to any particulartreatment and in particular were not mixed with fly ash and/or cokedust.

Table II shows that the eluate is acid and contains considerable amountsof undesirable components, in particular heavy metals, with a high COD(Chemical Oxygen Demand).

Table III shows the results of elution tests on five samples of residuesfrom pigment manufacture, which had been mixed with fly ash or coke inaccordance with the process according to the invention. The followingpoints are to be noted in relation to the individual samples:

The fly ash of sample 1 was an ash from a conventional brown coal dustfiring operation.

The fly ashes of samples 3 through 5 involved fly ashes from a browncoal fluidised bed firing operation.

Sample 2 involved the use of dust from brown coal low-temperature coke.

A forced-action mixer was used for mixing all the samples.

A comparison in respect of the values of Tables II and III shows that anoticeable reduction in the COD-value was attained in every case, thatis to say irrespective of whether coke or fly ash was added. In additionthe change in the pH-value is a matter of significance as both theaddition of fly ash and the addition of coke dust resulted in the eluatebecoming basic. That leads to the conclusion that even the basic ashcontent of the coke of sample 2 is sufficient to produce a noticeablechange in the pH-value although the extent of that change is clearlyless than in the case of the samples which had been mixed with fly ash.

Another point of significance is the reduction in the content of heavymetals in the eluate by virtue of mixing of the waste with basic browncoal fly ash.

The rise in the sulfate content, apart from sample 2, in relation to theuntreated samples of Table II, is evidently to be attributed to thesulfate content of the fly ash, in particular CaSO₄.

Pyrite sludges can be mixed in a similar fashion with fly ash and madefriable or capable of trickle flow. Besides being mixed with ash, pyritesludges are particularly suitable for mixing with brown coal or lignitecoke, possibly also brown coal or lignite dust, in order to producegranular friable substance which can be stored without problems overprolonged periods of time, and transported and handled withoutdifficulty in order in that form to be injected into a metallurgicalprocedure, for example a blast furnace procedure. As also in the case ofother substances, for example rolling scale sludge, that can be effectedin a simple fashion by way of the tuyeres of a blast furnace.

It is however also possible to briquette the resulting mixture which isproduced by carrying out the process in accordance with the invention,although that should desirably be effected no later than two to threedays after production of the resulting mixture. In that operation theresidual moisture present therein is used to bind the briquettes. Flyash, insofar as it has pozzuolanic properties, serves in that case as abinding agent.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE in the accompanying drawing is a diagrammatic view ofa preferred apparatus for carrying out the process in accordance withthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Rolling scale sludge which comes from a rolling mill is put intointermediate storage in a trough or other container 1. The rolling scalesludge 2 is moist and, besides oil and water, contains both metal andnon-metal impurities. Frequent metal impurities are for example wasteportions from the rolled material. Impurities of non-metal nature arepredominantly formed by articles which are thrown away in operation ofthe rolling mill, for example cleaning rag, plastic cups, paper and thelike. The sludge 2 frequently exhibits thixotropic properties which makeit necessary for it to be put into intermediate storage in the trough 1.

The sludge 2 is taken from the trough 1 by way of a conveyor section asindicated at 3 and fed To a mixing device 4 which advantageouslycomprises a forced-action mixer. The sludge 2 is taken from the trough 1in a batch-wise manner.

Depending on the size of the mixing device 4, for example 500 kg ofrolling scale sludge may be taken from the trough 1 and introduced intothe mixing device 4, every 5 through 10 minutes. The mixing device 4 issupplied by way of a metering screw 5 with additive substances which arestored in silos diagrammatically indicated at I, II and III. Thus forexample silo I may contain fly ash from a brown coal or lignite firingoperation. Silo II may be used to store coal or coke dust while silo IIImay be used to store other metal-bearing dusts, for example blastfurnace dusts which contain metal compounds. The additive substances arealso taken from silos I through III in a batch-wise manner in dependenceon the amounts of sludge 2 which are fed to the mixing device 4.

Whether additive substances are fed to the mixing device 4 from allthree silos I through III depends on the respective factors andparameters involved, in particular the composition and consistency ofthe sludge 2 and the subsequent use thereof. Thus it is possible foronly fly ash to be added to the sludge 2, from the silo I. It is alsopossible to provide a silo for quick lime. That will be desirable inparticular when using fly ash more especially from pit coal firingoperations, which contains no or few basic components. The ratio ofrolling scale sludge to the total amount of additive substances may befor example about between 2 and 5:1. The silos may be provided withsuitable metering units (not shown).

The mixing time in the mixing device 4 is generally between 1 and 10minutes, also depending on the nature of the sludge 2 and the amount ofadditive substance or substances added. After termination of the mixingoperation, the resulting mixture which represents the conditionedrolling scale sludge as indicated at 6 is discharged from the mixingdevice 4 and passed on to a grading device 7 which can be for example inthe form of a possibly multi-stage sieving or sifting device. Theresulting mixture 6 which leaves the mixing device 4 normally occurs inthe form of shall agglomerates which are for example of a grain size ofup to 4 mm. In the device 7 the impurities which generally comprisecoarser pieces are separated off. In that respect the arrangement may besuch that for example coarse metal and therefore magnetisable impuritiesare discharged at 10 while other, non-metal and thus non-magneticimpurities are discharged at 11.

The fine-grain material which passes through the sieve 7, as indicatedat 12, which predominantly comprises agglomerates of a maximum grainsize of for example about 4 mm, is put into intermediate storage, ifrequired, as indicated at 13. That may be desirable for example in orderfirstly to wait for the agglomerates to bind and set. The material 12 ispassed from the intermediate storage device 13, where provided, orpossibly otherwise directly from the grading device 7, into a silo 14which is connected by way of a valve 15 to a pressure vessel orcontainer 16. The vessel 16 has an outlet 17 which is communicated witha feed line 18 for a carrier gas. Respective predetermined amounts ofconditioned rolling scale sludge 6 are removed by means of the conveyorgas from the pressure vessel 16 through a discharge conduit 19 andinjected for example into the tuyere of a blast furnace or into a rotarycylindrical kiln or furnace for the production of cement. There are manypossible situations of use for re-utilisation of the conditioned,agglomerated rolling scale sludge 6.

When a sieve member is used in the grading device 7, it may be desirablefor the sieve member to be provided, at least over parts of its extent,on the top side thereof, with a cover in the form of a flexible mat. Themat may be formed for example by a portion of a conveyor belt whichentirely or predominantly consists of resilient material. Such a matwhich is low in weight in relation to unit of surface area is intendedto ensure that agglomerates which exceed a certain grain size are brokendown to the grain size which is desired for passing through the sievemember.

In a departure from the operating procedure illustrated by means of theapparatus in the accompanying drawing, the procedure may also be suchthat the resulting mixture issuing from the grading device 7, possiblyalso after being put into intermediate storage at 13, is fed to afurther mixer in which it is mixed with an additional granular substancewith which jointly the resulting mixture is fed to a thermal procedure.Thus it is possible to envisage that, when coal dust is injected throughthe tuyeres into the structure of a blast furnace, the conditionedrolling scale sludge or some other mixture as indicated above may be fedto a mixer, a chamber or other space from which the conditioned mixture,jointly with the coal, is pneumatically conveyed and then injected intothe blast furnace through its tuyeres. The way in which operation ismore specifically effected in that respect depends on the prevailingcircumstances, for example whether the carbonaceous material to beinjected into the blast furnace or similarly employed in some otherthermal procedure is suitable for conditioning of the mixture of wastematerials or whether it serves only to meet the C-requirement.

                  TABLE I                                                         ______________________________________                                        Pressure tests on pellets until first cracking occurs in the pellet                      d            h       Force                                         Sample No  (mm)         (mm)    (N)                                           ______________________________________                                        1          9.17         6.01    175                                           2          8.94         6.76    150                                           3          11.03        6.25    200                                           4          10.18        5.87    275                                           5          9.75         6.78    250                                           6          5.33         4.51    175                                           7          9.81         5.63    150                                           8          8.06         7.34    200                                           9          8.13         5.78    150                                           10         14.58        5.99    225                                           11         7.61         5.53    175                                           12         7.66         5.61    100                                           13         8.49         4.95    200                                           14         7.8          6.32    100                                           15         7.84         5.35    150                                           16         9.03         6.15    75                                            17         6.79         4.92    125                                           A          27.0         12.64   600                                           B          14.88        8.91    350                                           C          22.64        15.88   200                                           D          16.55        9.77    450                                           E          17.26        12.34   450                                           F          22.8         13.29   500                                           G          17.15        9.2     250                                           H          22.31        12.16   600                                           I          13.87        10.45   300                                           J          20.25        11.72   150                                           K          19.87        8.93    475                                           L          16.72        10.2    425                                           M          11.22        7.9     350                                           ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Analysis of the eluate of unconditioned iron-oxide                            bearing residues from pigment production                                                       Sample 1                                                                             Sample 2                                              ______________________________________                                        1. pH-value        4.6      4.7                                               2. Conductivity μS/cm                                                                         1.605    1.670                                             3. COD mgO.sub.2 /l                                                                              40       40                                                4. Sulfate content m/l                                                                           20       58                                                5. Chloride content mg/l                                                                         2200     675                                               6. Copper content mg/l                                                                           0.015    0.011                                             7. Nickel content mg/l                                                                           12       8.1                                               8. Zinc content mg/l                                                                             0.88     0.12                                              ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        Analysis of the eluate of conditioned agglomerated                            iron oxide-bearing residues from pigment production                           Sample No    1       2       3     4     5                                    ______________________________________                                        Amount of substance                                                                        54.00   58.00   56.65 51.86 53.45                                [g]                                                                           Moisture content [%]                                                                        7.45   13.76   11.75  3.59  6.45                                Dry substance [g]                                                                          49.98   50.02   50.00 50.00 50.00                                Amount of fly ash                                                                          22.7            16.6  8.8   16.6                                 Amount of brown coal 9.0                                                      coke dust                                                                     Measurement values                                                            in the eluate after                                                           24 hours                                                                      pH-value     11.2    6.7     9.3   9.6   8.9                                  Conductivity μS/cm                                                                       3.71    1.96    4.98  4.76  4.72                                COD mgO.sub.2 /l                                                                            31      <5      <5    13    15                                  Sulfate content mg/l                                                                        354    <10      798   769   814                                 Chloride content mg/l                                                                      1000     740    1320  1240  1140                                 Copper content mg/l                                                                        <0.01   4.1     <0.01 <0.01 <0.01                                Nickel content mg/l                                                                        <0.01   20.0    <0.01 <0.036                                                                              <0.019                               Zinc content mg/l                                                                          <0.005   0.62   <0.005                                                                              <0.005                                                                              <0.005                               ______________________________________                                    

It will be appreciated that the above-described examples and embodimentshave been set forth solely by way of illustration of the invention andvarious modifications may be made without departing from the scope andspirit of the invention.

What is claimed is:
 1. A process for converting a metal-containing wastematerial which is a mixture of solid and liquid material into a reusabledry product, the process comprising the steps of conveying the mixturefrom a container thereof into a forced action mixer and homogenizing themixture therein; passing a dry finely grained additive comprising one ormore additives selected from the group of fly ash, coal or coke dust, ablast furnace dust and quick lime from respective silos to the mixer,and mixing the homogenized mixture and the additive to form dryagglomerates having a grain size of up to about 4 mm and suitable forinfection into using a carrier gas into a thermal process.
 2. A processaccording to claim 1, wherein the homogenization is effected before theadditive is introduced into the mixer.
 3. A process according to claim1, wherein the finely grained dry additive has a grain size of between70 and 90 micron.
 4. A process according to claim 1, wherein theadditive is fly ash derived from brown coal or lignite.
 5. A processaccording to claim 1, wherein the mixture and the additive are mixed ina weight ratio of 2 to 5:1.
 6. A process according to claim 1, whereinthe mixture is selected from one or more of the materials of thefollowing group: rolling scale sludge, sludge residue from the pigmentindustry, black sludge from the processing of aluminum, sludge from theprocessing of pyrite, sludge comprising blast furnace gas dust, sludgefrom converters, sludge from grinding operations, sludge of from foundrydust, and sludge containing cutting machinery dusts.
 7. A processaccording to claim 1, wherein quicklime or a precursor thereof is addedbefore the mixture is mixed with the additive.
 8. A process according toclaim 1, including the step of subjecting the formed agglomerates to aclassification treatment to remove particles having a grain size above 4mm.
 9. A process according to claim 1, including the step of subjectingthe formed agglomerates to pelletisation.
 10. A process according toclaim 1, wherein a second waste material containing metal and comprisingsolid material and liquid material is mixed with the first-mentionedwaste material before mixing with the additive.
 11. A process accordingto claim 10, wherein the second waste material is mixed with thefirst-mentioned waste material in a ratio of about 3:1 by weight.
 12. Aprocess according to claim 1 including the step of injecting the dryagglomerates into a thermal process.
 13. A process according to claim 1including the step of injecting the dry agglomerates into a thermalprocess by means of a carrier gas.
 14. A process for converting amixture of solid and liquid waste material containing a metal into areusable product, the process comprising the steps of:homogenizing themixture; and mixing with the homogenized mixture a fine grained dryadditive selected from the group consisting of fly ash, coal coke andfurnace flue gas dust; whereby to produce agglomerates which aresufficiently dry to be sievable and injectable using a carrier gas intoa thermal process.
 15. A process according to claim 14 including thestep of injecting the agglomerates into a thermal process.
 16. A processaccording to claim 14 including the step of injecting the agglomeratesinto a thermal process by means of a carrier gas.
 17. A process for thetreatment of a first mixture of solid and liquid waste materials whichcontains at least one substance from the group consisting of metals andcompounds thereof, to improve its ability to be handled or reused,comprising the steps of homogenizing the first mixture, and adding tosaid first mixture and mixing therewith at least one finely divided drysubstance selected from the group consisting of fly ash, coke andfurnace flue gas dust to produce a resulting mixture at least part ofwhich can be graded or classified by sieving and is suitable forinjection using a carrier gas into a thermal process.
 18. A processaccording to claim 1, in which the homogenization of the first mixtureof waste materials is effected prior to mixing with said finely divideddry substance.
 19. A process according to claim 17 including the step ofinjecting said at least part of the resulting mixture into a thermalprocess.
 20. A process according to claim 17 including the step ofinjecting said at least part of the resulting mixture into a thermalprocess by means of a carrier gas.
 21. A process for the treatment of afirst mixture of solid and liquid waste materials which contains atleast one substance from the group consisting of metals and compoundsthereof to improve its ability to be handled or reused, comprising thesteps of homogenizing the first mixture, and adding to said firstmixture and mixing therewith at least one finely divided dry substanceselected from the group consisting of fly ash, coke and furnace flue gasdust to produce a resulting mixture at least part of which can be gradedor classified by sieving and is suitable for injection into a thermalprocess, in which said first mixture is primarily rolling scale sludge.22. A process for the treatment of a first mixture of solid and liquidwaste materials, which contains at least one substance from the groupconsisting of metals and compounds thereof to improve its ability to behandled or reused, comprising the steps of homogenizing the firstmixture, and adding to said first mixture and mixing therewith at leastone finely divided dry substance selected from the group consisting offly ash, coke and furnace flue gas dust to produce a resulting mixtureat least part of which can be graded or classified by sieving and issuitable for injection into a thermal process, in which said firstmixture is primarily rolling scale slurry containing oil.
 23. A processfor the treatment of a first mixture of solid and liquid waste materialswhich contains at least one substance from the group consisting ofmetals and compounds thereof to improve its ability to be handled orreused, comprising the steps of homogenizing the first mixture, andadding to said first mixture and mixing therewith at least one finelydivided dry substance selected from the group consisting of fly ash,coke and furnace flue gas dust to produce a resulting mixture at leastpart of which can be graded or classified by sieving and is suitable forinjection into a thermal process, in which said first mixture isprimarily rolling scale slurry containing more than 5 percentlubricating oil.